1. Field of the Invention
The present invention relates to an integrated control system for an electronically-controlled internal combustion engine and an automatic transmission, and specifically to technologies for optimally balancing two somewhat contradictory requirements, that is, better drivability and improved fuel consumption, while automatically controlling or regulating a driving torque to be transmitted via axle driveshafts to drive wheels and a transmission ratio (or a transmission speed-change ratio) on automotive vehicles with an electronic engine control module (ECM) or an electronic engine control unit (ECU), and an electronic componentry for transmission control, particularly suitable for a steplessly variable automatic transmission.
2. Description of the Prior Art
In recent years, there have been proposed and developed various controllers for an electronically-controlled internal combustion engine and a steplessly variable automatic transmission. More later-model cars with an electronically controlled engine and a continuously variable automatic transmission, require a high-accuracy control for both the driving torque transmitted to drive wheels and the speed-change ratio of the automatic transmission, to balance the better drivability and the improved fuel consumption. For example, Japanese Patent Provisional Publication Nos. 62-110536 and 62-110535 have disclosed controllers for controlling both a driving force (or an engine output torque) and a speed-change ratio of a belt type continuously variable automatic transmission often abbreviated to a "CVT". In the controller disclosed in the previously-noted Japanese Patent Provisional Publication No. 62-110536, a target driving torque is arithmetically calculated on the basis of both an accelerator opening (or an angular position of an accelerator pedal) and a vehicle speed. On the other hand, a target speed-change ratio (or a desired pulley ratio of the CVT) is arithmetically calculated on the basis of the calculated target driving torque and the vehicle speed. The speed-change ratio (the pulley ratio) of the CVT is feedback controlled, so that the actual pulley ratio of the CVT is adjusted toward the calculated target speed-change ratio. Also, a target engine torque (or a target engine output power) is retrieved from a predetermined characteristic map by reference to both the actual speed-change ratio of the CVT and the calculated target driving torque. A desired value of a control variable (e.g., a throttle opening) for a variable engine-torque control actuator, such as an electronically controlled throttle actuator, is retrieved from a predetermined characteristic map by reference to both the retrieved target engine torque and the actual engine speed. The variable engine-torque control actuator, that is, the throttle actuator, is feedback controlled, so that the desired value of a control variable (e.g., the desired throttle opening) is reached. The previously-discussed prior art controller is constructed, so that the target speed-change ratio is retrieved from the predetermined characteristic map by reference to the target driving torque and the vehicle speed. That is, the characteristic map for retrieval of the target driving torque and the characteristic map for retrieval of the target speed-change ratio are mutually related to each other. When the characteristic map of the target driving torque has been altered to properly tune the drivability of the vehicle, the target speed-change ratio retrieved by reference to both the target driving torque retrieved and the vehicle speed, would be changed as a result of alteration of the target-driving-torque characteristic map. As is generally known, the characteristics defined by the target-speed-change-ratio map exert a great influence on fuel economy. As set out above, in the prior art controller as disclosed in the Japanese Patent Provisional Publication No. 62-110536, it is difficult to balance both enhanced drivability and improved fuel consumption, since the target-driving-torque map and the target-speed-change-ratio map cannot be set or altered independently of each other. In addition, in the prior art controller disclosed in the Japanese Patent Provisional Publication No. 62-110536, the target engine torque is retrieved by reference to only two factors, namely the actual speed-change ratio and the target driving torque. Thus, the target engine torque could not be precisely compensated for, depending on engaging and disengaging conditions of a releasable coupling device or an engagement/disengagement device, such as a computer-controlled clutch placed between the engine and the CVT automatically to couple the engine and the CVT at least during vehicle travel and to uncouple them at least during vehicle stand-still. For example, the computer-controlled clutch corresponds to a so-called start clutch (an electromagnetic clutch) for the CVT or a hydraulically-actuated lock-up clutch employed in a so-called lock-up torque converter capable of engaging automatically to lock the impeller and turbine wheels together to give a direct drive at a predetermined ratio of turbine-to-engine speed. For the reasons set forth above, in the prior art controller, there is another problem of lowering of the accuracy of driving-torque control, when the computer-controlled clutch (the releasable coupling device or the engagement/disengagement device) is disengaged and thus there is the difference of relative speed between input and output shafts of the computer-controlled clutch. On the other hand, the Japanese Patent Provisional Publication No. 62-110535 discloses a driving-torque controller suitable for an automobile power train employing a so-called lock-up torque converter. In the Japanese Patent Provisional Publication No. 62-110535, a target engine output horsepower is arithmetically calculated on the basis of both an accelerator opening and a vehicle speed. A target input-shaft rotational speed of the CVT is arithmetically calculated on the basis of the calculated target output horsepower. The input-shaft rotational speed of the CVT is feedback controlled, so that the actual input-shaft rotational speed of the CVT is adjusted toward the calculated target input-shaft rotational speed through a speed-change ratio control of the CVT. On the other hand, a target engine torque is arithmetically calculated on the basis of both the calculated output horsepower and the actual input-shaft rotational speed of the CVT. The engine output torque is feedback controlled, so that the calculated target engine torque is reached through an engine control, concretely a throttle-opening control. In the controller disclosed in the Japanese Patent Provisional Publication No. 62-110535, there is a problem that the characteristic map for retrieval of the target output horsepower and the characteristic map for retrieval of the target input-shaft rotational speed are mutually related to each other. Thus, these characteristic maps cannot be tuned independently of each other, since the content of one of the two maps is affected by alteration (rewriting) of the content of the other map. Also, the control system disclosed in the Japanese Patent Provisional Publication No. 62-110535, may provide a high-accuracy driving-torque feedback control, effectively reducing a fuel-consumption rate, under a specified condition where the torque converter assumes a full lock-up mode at which there is no difference of relative speed between input and output shafts of the torque converter with the lock-up clutch strongly engaged. However, when the torque converter assumes an open converter mode at which the lock-up clutch is completely released, or a slip lock-up mode at which the lock-up clutch is partially engaged, there are remarkable fluctuations in both the input torque and the output torque of the torque converter, and thereby it is difficult to provide a high-accuracy driving-torque feedback control.